Various neutron-gamma spectroscopy techniques are based on the use of neutrons to create excited states in a nucleus which then decays via emission of one or more gamma-rays. The gamma-rays of each isotope have a characteristic energy spectrum which may be used to distinguish an elemental concentration.
The neutrons can be generated either by isotopic sources like 241AmBe or 252Cf, or alternatively by an electronic neutron generator. The neutron generator may use the d-T reaction for the neutron generation, but other neutron reactions may be used. The neutron generator may be pulsed, i.e., it emits bursts of neutrons in a defined sequence. This may allow it to distinguish between capture and inelastic gamma-rays and may make it possible to determine additional quantities of interest, such as, for example, slowing down time, the geologic formation or borehole thermal neutron capture cross section, geologic formation bulk density (neutron-gamma density), and others.
Gamma-rays may be detected in gamma-ray detectors spaced away from the neutron generator. These gamma-ray detectors measure the spectrum of gamma-ray energies deposited in the detector material. Suitable detectors may be scintillation detectors or other gamma-ray detectors that have a desired detection efficiency and spectral performance.